feat(tvix/build): add BuildService trait

Also provide a dummy implementation that just fails on any build that's
requested.

Change-Id: I0df743a730c5331ec9ce6e97a966abe18ce067f5
Reviewed-on: https://cl.tvl.fyi/c/depot/+/10627
Autosubmit: flokli <flokli@flokli.de>
Reviewed-by: raitobezarius <tvl@lahfa.xyz>
Tested-by: BuildkiteCI

tvix/Cargo.lock

@@ -3291,6 +3291,7 @@ dependencies = [
  "tonic 0.10.2",
  "tonic-build",
  "tonic-reflection",
+ "tracing",
  "tvix-castore",
 ]
 

tvix/Cargo.nix

@@ -10246,6 +10246,10 @@ rec {
             packageId = "tonic-reflection";
             optional = true;
           }
+          {
+            name = "tracing";
+            packageId = "tracing";
+          }
           {
             name = "tvix-castore";
             packageId = "tvix-castore";

tvix/build/Cargo.toml

@@ -10,6 +10,7 @@ prost = "0.12.1"
 thiserror = "1.0.56"
 tonic = "0.10.2"
 tvix-castore = { path = "../castore" }
+tracing = "0.1.37"
 
 [dependencies.tonic-reflection]
 optional = true

tvix/build/src/buildservice/dummy.rs

@@ -0,0 +1,19 @@
+use tonic::async_trait;
+use tracing::instrument;
+
+use super::BuildService;
+use crate::proto::{Build, BuildRequest};
+
+#[derive(Default)]
+pub struct DummyBuildService {}
+
+#[async_trait]
+impl BuildService for DummyBuildService {
+    #[instrument(skip(self), ret, err)]
+    async fn do_build(&self, _request: BuildRequest) -> std::io::Result<Build> {
+        Err(std::io::Error::new(
+            std::io::ErrorKind::Other,
+            "builds are not supported with DummyBuildService",
+        ))
+    }
+}

tvix/build/src/buildservice/mod.rs

@@ -0,0 +1,12 @@
+use tonic::async_trait;
+
+use crate::proto::{Build, BuildRequest};
+
+mod dummy;
+pub use dummy::DummyBuildService;
+
+#[async_trait]
+pub trait BuildService: Send + Sync {
+    /// TODO: document
+    async fn do_build(&self, request: BuildRequest) -> std::io::Result<Build>;
+}

tvix/build/src/lib.rs

@@ -1 +1,2 @@
+pub mod buildservice;
 pub mod proto;